Towing apparatus

ABSTRACT

A towing apparatus is disclosed capable of moving aircraft and other workpieces about an airfield or other workspace. The present invention includes a first frame which is rotatable relative to a second frame about a common substantially vertical axis. A wheel assembly is positioned within the first frame and driven by a motor which is also mounted on the first frame. A gripper assembly for engaging the aircraft or other workpiece is attached to the second frame. In this manner, the present invention provides for the towing of aircraft or other workpieces along an axis which is proximate the axis of the wheel assembly. Additionally, it provides for a low center of gravity significantly enhancing the stability and maneuverability of the present invention in a towing attitude or a non-towing attitude.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus for towing aworkpiece. More particularly, the present invention relates to amotorized tractor-towing apparatus of enhanced stability capable oftowing an airplane, trailer, or other workpiece.

[0003] 2. Description of the Related Art

[0004] It is frequently necessary to move closely-parked privateaircraft, for example, around an airfield or within a hanger. State ofthe art devices disclose tractors having some capability of moving suchaircraft but are unstable, particularly when pulling a heavy workpiece,such as an aircraft. See, for example, U.S. Pat. Nos. 3,819,001 and3,861,483. Because of their unstable nature, such prior art devicesrequire a stabilizer bar or other mechanism to stabilize it and make itmore maneuverable particularly in a towing attitude. However, suchadditional structure makes the prior art devices particularly difficultto operate in congested conditions such as those frequently found atprivate airfields.

[0005] Other prior art aircraft handling and towing devices arecumbersome and do not provide for sharp turning radii required inmaneuvering aircraft about a congested airfield, for example. See U.S.Pat. Nos. 3,049,253; 2,732,088; 2,734,716; 3,038,550; 3,662,911;4,318,448; and 4,576,245.

[0006] Additionally, there exists the need for an enhanced grippermechanism to attach to the nosewheel or tailwheel of an aircraft in asecure manner and yet operate with a small turning radius. Prior artdisclosures, such as U.S. Pat. Nos. 2,874,861 and 2,877,911, do notpermit the type of gripping necessary for a tight turning radiusoperation with enhanced locking capability.

[0007] Accordingly, the need exists for an improved towing apparatus foraircraft and other workpieces which is stable even when not towing aworkpiece. However, once engaged to either a nosewheel or a tailwheel ofan aircraft for example, the device provides for a tight turning radiusand is easy to maneuver in forward or reverse.

SUMMARY OF THE INVENTION

[0008] The present invention is an apparatus for towing a workpiece,such as an aircraft. The apparatus comprises first and second frameswhich are in spaced vertical relationship to one another. The frames areattached in such a manner that the first frame rotates relative to thesecond frame about a common substantially vertical axis. A wheelassembly is supported by the first frame and includes a wheel forrotational movement about a first axis. A motor is used to power thewheel assembly. A handle assembly is attached to the first frame toenable the operator to rotate the first frame relative to the secondframe. A gripper assembly is supported by the second frame and offsetfrom the vertical axis. The gripper assembly is positioned on the secondframe to engage a workpiece for towing along a second axis which ispositioned above or below the first axis by no more than about 30% ofthe radius of the wheel. In this manner, the present invention providesa low center of gravity and permits the towing axis, or the workingaxis, to be at or near the rotating axis of the wheel. Thus, a stabletowing apparatus is provided which permits the workpiece, such as thenosewheel or tailwheel of an aircraft, to be in close proximity to thewheel of the present invention. Consequently, the turning radius issmall.

[0009] The present invention may also include a transmission, such as ahydrostatic transmission, positioned between the motor and the wheelassembly to enable the transmission of power from the motor to the wheelon a smooth basis and permit motorized forward and rearward motion ofthe towing apparatus and the workpiece.

[0010] The gripper assembly of the present invention may be used to towthe nosewheel of an aircraft or another wheel of a workpiece.Alternatively, the gripper assembly may be used to tow the tailwheel ofan aircraft. If the nosewheel of an aircraft is being pulled, it may bepreferable to permit the nosewheel to remain in contact with the groundwhile the present invention tows the aircraft. In this event, thegripper assembly is supported by the second frame and includes astationary arm and a pivotal arm. The pivotal arm is rotated relative tothe second frame. Once engaged the ends of both the first and secondarms compress the axis of a nosewheel to permit a pulling or pushingtowing operation by the present invention. The gripper assembly may alsoinclude a gas cylinder, for example, positioned between the first andsecond arms to dampen any movement between the ends of either arm andthe nosewheel thereby further securing the first arm relative to thesecond arm.

[0011] In the event the present invention is intended to engage thetailwheel of an aircraft, the gripper assembly may include a tow framesupporting a cradle. The gripper assembly may include means to tilt oneend of the tow frame toward the ground enabling the cradle to engage andsupport the tailwheel. The gripper assembly may also include means foractivating the tilt means to lower one end of the tow frame and thenraise that same end thereby elevating the tailwheel off the ground andpermitting the present invention to tow the aircraft along a towing axispositioned between about 60% of the radius of the wheel of the presentinvention above the axis of that wheel to about 60% of the radius ofthat wheel below the rotational axis of the wheel.

[0012] Thus, the present invention provides a stable pushing and pullingtowing apparatus for a workpiece such as an aircraft that provides for asharp turning radius, forward and rear motion, and the introduction ofsubstantial power in a forward or rearward direction on a smooth andcontinuous basis.

[0013] The more important features of this invention have beensummarized rather broadly in order that the detailed description may bebetter understood. There are, of course, additional features of thepresent invention which will be described hereinafter and which willalso form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more fully describe the drawings used in the detaileddescription of the present invention, a brief description of eachdrawing is provided.

[0015]FIG. 1 is an elevation view of the present invention.

[0016]FIG. 2 is an elevation view of the present invention from theopposite side shown in FIG. 1.

[0017]FIG. 3 is a cross-sectional view of the present invention takenalong line 3-3 of FIG. 1.

[0018]FIG. 4 is a detailed cross-sectional view taken along line 4-4 ofFIG. 3.

[0019]FIG. 5 is a bottom view of a portion of the present invention.

[0020]FIG. 6 is a view similar to FIG. 5 but in a different operationalsequence from that shown in FIG. 5.

[0021]FIG. 7 is a top view of an alternate embodiment of a portion ofthe present invention.

[0022]FIG. 8 is an elevation view of the alternate embodiment shown inFIG. 7.

[0023]FIG. 9 is a different operational sequence of the alternateembodiment shown in FIG. 8.

[0024]FIG. 10 is a top view of another alternate embodiment of a portionof the present invention.

[0025]FIG. 11 is a partial top view of a portion of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Referring to FIGS. 1-4, the present invention is a towingapparatus 20 having a first frame 22 and a second frame 24. Each frame22 and 24 is generally rectangular in configuration. In the case offrame 22, it is shown to include longitudinal members 26 and transversemembers 28. Second frame 24 includes longitudinal members 30 and atransverse member 32. The present invention also includes a handleassembly 38 having a member 39 which is attached to first frame 22 atpin connection 40. Member 42 serves to brace member 39 to first frame22.

[0027] Referring still to FIGS. 1-4, a motor 44 is attached to, andsupported by, first frame 22. Motor 44 may be a conventional internalcombustion motor such as a lawnmower motor. In the prototype of thepresent invention, the motor is a 3.5 horsepower Briggs & Strattonengine, readily commercially available. Alternatively, motor 44 may beanother type of motor such as an electric motor or an air motor.Obviously, in such cases the user would need to provide a power sourcesuch as electricity or compressed air through a power cord or air hoseup to motor 44. In the case of an internal combustion engine as shown, athrottle 46/cable 48 is attached to handle 38 and connects with thethrottle setting of motor 44 to power up or down motor 44. The throttle46/cable 48 assembly is well known to those skilled in the art and issimilar to that found on commercially-available lawnmowers.

[0028] The present invention also includes a wheel assembly 50 which isrotatably supported within first frame 22. Referring to FIGS. 3 and 4,wheel assembly 50 includes a wheel/tire 52. Axle 54 passes through wheel52 and is rotatably supported in the preferred embodiment by flanges 56which are attached to longitudinal members 26 of first frame 22. Eachend of axle 54 is held in place by a hub 58 having a lynch pin 60 orother fastener such as a set screw. A sprocket 62 is attached to axle 54and fixed relative to axle 54 and wheel 52. In this manner, wheel 52rotates about axle 54, but within first frame 22.

[0029] Referring back to FIGS. 1-2, the present invention may include atransmission 64, preferably a hydrostatic transmission, such as thatmanufactured by the Eaton Corporation, model no. C-250-801. Such ahydrostatic transmission is well known to those skilled in the art andcommonly used on riding lawnmowers, garden tractors and off-roadvehicles. Such a transmission serves to provide a gradual increase anddecrease in power from motor 44 and transfer that power to a wheelassembly 50 in accordance with the present invention as described below.In addition, such a transmission provides for motorized forward andrearward motion.

[0030] Power is transferred from motor 44 to transmission 64 by means ofa belt 66. As shown in FIG. 2, belt 66 passes around drive pulley 68 ofmotor 44 and pulley 70 of transmission 64. In accordance with theoperation of the present invention as will be described in more detailbelow, the power output side of transmission 64 is shown in FIG. 1 asdrive shaft 72. Shaft 72 is connected to a sprocket 74. A chain 76 isused to drivably engage sprocket 74 with sprocket 62 thereby rotatingwheel 52 and driving the present invention.

[0031] Referring still to FIGS. 1-4, but in particular FIGS. 1 and 4,second frame 24 is rotatably supported relative to first frame 22 byconcentric drums 78 and 80. As shown in FIG. 2 and as noted above,second frame 24 comprises longitudinal members 30. Each longitudinalmember 30 is fixedly attached to outer drum 80. Outer drum 80 is acylindrical member which is vertically supported by, and rotates within,inner drum 78. Drum 78 is securely attached to members 26 of first frame22. Referring still to FIGS. 1 and 4, it can be seen that outer drum 80is supported vertically by shoulder 82 of inner drum 78. Thus, secondframe 24 can rotate relative to first frame 22 since outer drum 80 canrotate about inner drum 78 about a full 360°. If desirable, second frame24 may be locked to first frame 22 by a bracket 84 which is pivotablyattached at connection 86 to first frame 22. When it is desirable topermit the rotation of the first frame 22 relative to the second frame24, in accordance with the operation of the present invention asdescribed below, the operator pulls knob 88 upwardly displacing cable 91and thereby pivoting bracket 84 about connection 86. Thus, bracket 84releases first frame 22 relative to second frame 24 enabling therotational movement of first frame 22 relative to second frame 24.

[0032] Referring still to FIGS. 1 and 2 and now FIGS. 5 and 6, thepresent invention also includes a gripper assembly 90 which is used toengage a workpiece. In the case of FIGS. 1-6, the workpiece as shown inphantom lines is a wheel 92, such as the nosewheel of an aircraft.Obviously, it will be apparent to one skilled in the art that wheel 92may be the wheel of a workpiece other than an aircraft. Gripper assembly90 comprises a first arm 94 and second arm 96. Referring to FIG. 5(which is a bottom view looking upwardly), first arm 94 is fixedlyattached to second frame 24. First arm 94 includes a longitudinal member97 which is shown bolted to longitudinal member 30 of second frame 24. Asleeve 100 is attached at one end to member 97 and a pin 98 is adaptedto pass through sleeve 100. Pin 98 is bolted by screw 102 to sleeve 100.A hub 104 is attached at one end of pin 98. Hub 104 includes a recessand is selected in size to pass over the axle or wheel hub 106 ofnosewheel 92.

[0033] Referring still to FIG. 5, second arm 96 of gripper assembly 90is pivotably connected to frame 24 at pin connection 108. The second arm96 also includes a hub 126/pin 128 arrangement similar to that describedearlier with respect to hub 104/pin 98 of first arm 94. Again, hub 126engages wheel hub 130 of nosewheel 92. A linkage assembly 110 supportedby second frame 24 is used to pivotably rotate second arm 96 relative tosecond frame 24. Linkage assembly 110 includes a lever arm 112 attachedat one end to pin connection 108 and at its other end 114 to rod 116.Rod 116 is in turn pivotably connected to handle 118 at connection 120.Handle 118 is pivotably connected and supported by bracket 124 at pinconnection 122. Bracket 124 is welded directly to drum 80 as arelongitudinal members 30 of second frame 24. The selection of the lengthof bracket 124 from drum 80 to pin connection 122 is such that whenhandle 118 is rotated about pin connection 122 to the closed position asshown in FIG. 6, an over-the-center locking action occurs which preventshandle 118 from being prematurely released except by the operatorphysically moving handle 118 back to the position shown in FIG. 5. Thisresults in the locking of nosewheel 92 relative to said second frame 24.The gripper assembly 90 may also include a dual-acting gas cylinder 132which serves to provide compressive resistance in either direction. Itis attached at one end 134 to second frame 24 and at its other end 136to lever arm 112. When handle 118 is rotated to the position shown inFIG. 6 enabling the engagement of second arm 96 against hub 130 of wheel92, shaft 138 of gas cylinder 132 is extended thereby resisting anymovement of second arm 96 relative to second frame 24 as may be causedby any jarring or bouncing movement of nosewheel 92. Yet cylinder 132serves to permit extreme movement of the end of second arm 96 at hub 126which may occur if nosewheel 92 hits a pothole or other obstruction onthe airfield while being towed. This permits the emergency release ofthe nosewheel 92 without damaging the nosewheel axle or nosewheelundercarriage assembly.

[0034] Referring back to FIG. 2, as discussed above transmission 64receives its input power from belt 66. Transmission 64 provides forwardor rearward direction of the present invention by placement of lever 142in a forward or rearward direction as discussed herein. This is themechanism most commercially available hydrostatic transmissions use toshift the direction of rotation of its drive shaft. The Eaton modelemployed in the prototype of the present invention provides for forwardor rearward motion by shifting the rotation of drive shaft 72 from aclockwise revolution to a counterclockwise revolution, depending on theorientation of lever 142.

[0035] Referring to FIGS. 2 and 11, handle linkage assembly 140 includesa handle 144 which enables the operator to pull up on either side ofhandle 144 activating the forward and rearward direction of the presentinvention in accordance with the foregoing description. Handle 144 ispivotably bolted at connection 146 to member 39 and to a transversemember 147. Member 147 is pivotally connected to link 148. Link 148 isin turn connected to a link 150 through a triangular plate 152. Link 150is pivotably connected to rod 153, and rod 153 connects to lever 142.

[0036] Referring to FIG. 2, the present invention also includes amechanism to return handle 144 to a centered position as shown in FIGS.2 and 11. That mechanism is shown in FIG. 2 as centralizer system 151.Link 150 is also pivotally attached at connection 154 to member 155.Member 155 is pivotally connected to a vertical member 157 (FIG. 3) atpin connection 159. Vertical member 157 is fixed to first frame 22. Inthis manner, member 155 pivots about connection 159 as handle 144 ispulled. Centralizing system 151 also includes a camming member 162 whichis fixedly attached at connection 164 to vertical member 157. Cammingmember 160 pivots at connection 164 and is restrained at its other endby spring 170. In this manner, when either end of handle 144 is pulledand released, the notched portion 161 of camming member 162 serves toreturn member 155 to the vertical position as shown in FIG. 2. This thenserves to return link 150 to its neutral position and also handle 144 tothe neutral position as shown in FIG. 11.

[0037] In addition to the centralizer system 151 shown in FIG. 2, atensioner system 163 is also shown in FIG. 2 which serves to ensureadequate tension is maintained on belt 66. This is achieved through apulley 168 which is supported by member 166. Member 166 is in turnpivotally connected to vertical member 157, and the other end of member166 is forced in a downward position by compression spring 172. Pulley168 is urged against the top of belt 66 to ensure that belt 66 remainstight against both pulleys 68 and 70.

[0038] The operation of transmission 64 to drive the present inventionis as follows. When the operator pulls up or squeezes the right handportion of handle 144 as shown in FIG. 11, links 148 and 150 areadvanced forwardly. This in turn advances rod 153 and lever 142 forward.Advancement of lever 142 forward causes the rotation of drive shaft 72(see FIG. 1) of the Eaton transmission selected to rotate in a clockwisedirection. This in turn causes the clockwise rotation of sprocket 62which advances the present invention forward. Similarly, when theoperator pulls up on the left hand portion of handle 144 as shown inFIG. 11, links 148 and 150 and rod 153 are advanced rearwardly which inturn causes lever 142 to move to the right as shown in FIG. 2. Thiscauses the Eaton transmission to rotate drive shaft 72 in acounterclockwise direction providing for rearward motion of the presentinvention. Thus, whether the operator is pulling up on the left or righthand portion of handle 144 will determine whether the present inventionmoves in a forward or rearward direction. If the operator is not pullingup on either portion of handle 144, the lever 142 remains in a neutralposition as shown in FIG. 2 due to the centralized system 151 andsprocket 74 of transmission 64 does not rotate.

[0039] Referring now to FIGS. 7-10, alternate embodiments of the gripperassembly are shown. Gripper assembly 290 is intended to be used on aworkpiece such as the tailwheel of an aircraft. In the case of anaircraft which has a tailwheel (also known as a “tailtragger”), theremust be sufficient horizontal distance from the tailwheel of theaircraft to the end of its rudder to clear the towing apparatus. Thus,gripper assembly 290 includes longitudinal members 294 and 296. Unlikethe preferred embodiment of gripper assembly 90, longitudinal members294 and 296 do not pivot relative to one another. Rather, they arebolted to longitudinal members 30 of second frame 24 by bolts 295. Whilelever arm 112 and rod 116 of locking assembly 110 are shown in FIG. 7,they are not used. Longitudinal members 294 and 296 are held fixedrelative to one another by cross members 298. A cradle 300 is providedhaving members 301, 302, 303. Cradle 300 is used to support thetailwheel 292 of the aircraft, or similar workpiece. Members 294 and 296include apertures 305. Pins are provided at each end of member 302 andare adapted to fit within corresponding apertures 305 enabling theoperator to select the size of opening 310 so as to accommodate aparticular size tailwheel 292.

[0040] Referring still to FIGS. 7 and 8, assembly 290 includes sled 312having longitudinal members 314 adapted to slide relative to members 294and 296. Sled 312 supports a hydraulic jack 316 which is in fluidcommunication by hose 315 to a hydraulic ram 318. Members 320 areprovided which connect at one end 321 to a flange 322 of each member314. The other end of each member 320 is pivotally connected to arotating arm 324. A wheel 326 is attached to one end of each arm 324.Each arm 324 is pivotally supported by a member 294 or 296 at pinconnection 327.

[0041] In the operation of this alternate embodiment, the operatorreleases all pressure from hydraulic jack 316 which permits sled 312 toslide to the left as shown in FIG. 7. This results in the pivotalmovement of wheel 326 about pin connection 327, thereby lowering end 400of gripper assembly 290 as seen in FIG. 9. In this lowered position, theoperator may advance the present invention under a tailwheel 292 intospace 310 defined by cradle 300. The operator then pumps handle 317 ofjack 316 introducing hydraulic pressure into ram 318 and advancingpiston 319 to the right as shown in FIG. 7. Such movement of piston 319to the right causes sled 312 also to move to the right. This causes thepivotal movement of wheels 326 in a clockwise direction about connection327 until an elevated position is achieved as shown in FIG. 8. Thepresent invention may then be used to tow the aircraft as describedbelow in more detail below.

[0042] Referring to FIG. 10, an alternate embodiment of gripper assembly292 as seen in FIG. 7 is depicted. In this alternate embodiment, gripperassembly 292′ includes a mechanical linkage assembly 401 in place ofhydraulic jack 316/hydraulic ram 318 as shown in FIG. 7. Linkageassembly 401 includes a handle 402 pivotally attached to sled 312 at pinconnection 404. Handle 402 is connected to member 406 at connection 407.The other end of member 406 is attached to a cross member 298. Thus,rather than pumping a handle 317 to displace a piston 319 and move sled312 as discussed above with respect to FIGS. 7 and 8, the operatorrotates handle 402 about pivot connection 404. If handle 402 is in theposition shown by solid lines in FIG. 10, the end 400′ of gripperassembly 292′ is in the position shown in FIG. 9. Once the operator haspositioned the present invention under a tailwheel within cradle opening310′ as discussed above, the operator rotates handle 402 to the positionshown by phantom lines in FIG. 10. This causes the advancement of sled312′ to the right as shown in FIG. 10 and elevates wheels 326′ to theposition shown in FIG. 8. The operator would then be in the position ofmoving the aircraft in accordance with the present invention asdescribed below.

OPERATION OF THE PRESENT INVENTION

[0043] In the operation of the present invention, the operator startsmotor 44. The throttle would be placed initially in an idle position andhandle 144 would be in a neutral position as seen in FIG. 11. As notedabove, the present invention provides that wheel assembly 50 is fixedrelative to first frame 22, but can rotate about a first axis 501defined by axle 54. Similarly, outer drum 80 rotates relative to innerdrum 78 about a common substantially vertical axis 502 which, forpurposes of FIG. 1, is shown as passing through the center of axle 54 ofwheel 52 because wheel assembly 50 is positioned in the center of drums78/80. However, it is not essential that axis 502 intersect axle 54 forthe successful operation of the present invention.

[0044] If gripper assembly 90 is used, the operator throttles up motor44 using throttle 46. If the operator wished to move the presentinvention in a forward direction, the operator would squeeze the righthand portion of handle 144 thereby advancing lever 142 forward. Sincelever 142 is moved in a forward direction, drive shaft 72 rotates in aclockwise direction which therefore rotates sprocket 62 in a clockwisedirection and moves the present invention forward. To move the presentinvention in reverse, the operator squeezes the left-hand portion ofhandle 144 which moves lever 142 rearward and causes thecounterclockwise rotation of drive shaft 72.

[0045] Preferably, bracket 84 remains in the locked position as shown inFIG. 1 while the present invention is being maneuvered about in anon-towing mode. However, when it is time to attach gripper assembly 90to a workpiece, knob 88 is rotated upwardly pivoting bracket 84 aboutbolt connection 86 thereby permitting relative movement of the firstframe 22 relative to the second frame 24.

[0046] Referring to FIG. 5, if the preferred embodiment of gripperassembly 90 is used, the operator advances gripper assembly 90 to theposition shown in FIG. 5 and engages hub 104 against axle hub 106 ofnosewheel 92, for example. At that point, the operator rotates lever 118into a locked position as shown in FIG. 6 advancing hub 126 of secondarm 96 against hub 130 of the nosewheel. In this position, the gripperis fully engaged and gas cylinder 132 provides additional load furthersecuring arm 96 against hub 130. With bracket 84 disengaged, theoperator may easily rotate the first frame relative to second frame asshown in FIG. 6. Since wheel 52 has a single point of contact againstthe ground, it is very easy to rotate the present invention aboutvertical axis 502. In FIG. 6, first frame 22 has only been rotated about45° relative to its original position; however, it will be understood byone skilled in the art that first frame 22 may be rotated virtually 360°relative to its original position or with reference to second frame 24.The only obstruction that may limit its rotation is that handle assembly140 may contact the workpiece. However, except for this limitation,first frame 22 may rotate 360° relative to second frame 24.

[0047] Referring back to FIG. 6, once the operator has moved first frame22 to a particular angle relative to second frame 24, the left portionof handle 144 is pulled upwardly thereby advancing lever 142 to theright as shown in FIG. 2 which is the reverse mode. This means thatdrive shaft 72 would rotate in a counter clockwise direction which inturn rotates sprocket 62 in a counterclockwise direction and causes thepresent invention to move in a reverse direction, i.e., it is pullingthe aircraft. Moving in a reverse direction enables the operator toadvance the workpiece rearwardly and easily maneuver it.

[0048] Since the present invention is balanced, it is very easy tooperate. As can be seen, the weight of transmission 64 largely balancesthe weight of the motor 44 about vertical axis 502. In this manner, thepresent invention is very easy to handle. Additionally, sincetransmission 64 and motor 44 are close to the ground, the presentinvention is very stable.

[0049] It will be apparent to one skilled in the art that the presentinvention provides means to simultaneously power and rotate first frame22 relative to second frame 24 without the need to lift any portion ofwheel 52 off the ground. Additionally, the present invention provides avery stable design since it has a low center of gravity. Furthermore,the present invention provides for the towing of a workpiece along anaxis 503 (occasionally referred to as a second axis) which is generallyco-linear with the point-of-contact of the nosewheel of the workpiece,for example, and the point-of-contact of second frame 24 with drum 80.The present invention provides for the placement of axis 503 proximateaxis 501 of wheel 52. By positioning the tow axis 503 proximate axis 501of wheel 52 enhanced stability is achieved not found in the prior art.For example, in both U.S. Pat. Nos. 3,819,001 and 3,861,483, the priorart devices are unstable due to the significant vertical distancebetween the towing axis from the rotational axis of the wheel. Thiscreates a large moment which therefore requires a stabilizing system asnoted therein.

[0050] In the present invention, it has been found preferable toposition axis 503 no more than between about 60% of the radius of wheel52 above to about 60% of the radius of wheel 52 below axis 501. Thisrelationship is shown in FIG. 4 wherein “r” represents the radius ofwheel 52 and α represents about 60% of “r”. As used herein, the term“wheel” includes the tire. More preferably, α is about 40% of “r”, andmost preferably, α is about 20% of “r”.

[0051] Additionally, the present invention provides for a very shortturning radius—the distance from the contact point of wheel 52 with theground and the axle of nosewheel 92. This is also a significantadvantage because it permits very sharp turns. In fact, the operatorcould move first frame 22 90° to 160° off center and then move theaircraft very sharply.

[0052] In the use of the alternate gripper assemblies 290 and 290′, arms94 and 96 of gripper assembly 90 are disconnected at bolts 99 as shownin FIG. 5, and arms 294 and 296 are connected to members 30 with bolts295. If the embodiment shown in FIG. 7 is used, the operator wouldrelease pressure within jack 316 allowing sled 312 to slide to the leftas shown in FIG. 7 permitting wheels 326 to pivot about connection 327as seen in FIG. 9. This lowers end 400 of gripper assembly 290. Theoperator would then advance the present invention by pulling on handle144 to move the present invention in a forward direction. This wouldadvance end 400 under a tailwheel until it rests within cradle opening310. At that point, the operator pumps handle 317 moving piston 319 tothe right which causes sled 312 to move to the right. Wheels 326 thenrotate about connection 327 until in an upright position as shown inFIG. 8. At that point, the operator may move the present invention in arearward direction as described above and easily maneuver the aircraftabout the airfield or within a hanger or other confined space.

[0053] If gripper assembly 290′ is used as shown in FIG. 10, theoperator would simply place handle 402 in the position shown by solidlines. This lowers gripper assembly 290′ to the position shown in FIG.9. Once the tailwheel is positioned within cradle opening 310′, theoperator moves handle 402 to the position shown by phantom lines in FIG.10. This elevates gripper assembly 290′ to the position shown in FIG. 8.Once again, the operator is then free to operate the present inventionas described above.

[0054] The foregoing invention has been described in terms of variousembodiments. Modifications and alterations to these embodiments will beapparent to those skilled in the art in view of this disclosure. It is,therefore, intended that all such equivalent modifications andvariations fall within the spirit and scope of invention as claimed.

What is claimed is:
 1. An apparatus for towing a workpiece comprising: afirst frame; a second frame in spaced vertical relationship to the firstframe; means for attaching said first frame to said second frameenabling rotational movement of said first frame relative to said secondframe about a common substantially vertical axis; a wheel assemblysupported by said first frame and having a wheel for rotational movementabout a first axis; a motor to power said wheel assembly; a handleassembly attached to said first frame to rotate said first framerelative to said second frame; and a gripper assembly supported by saidsecond frame and offset from said vertical axis, said gripper assemblybeing positioned on said second frame so as to engage a workpiece fortowing along a second axis positioned above or below the first axis byno more than about 60% of the radius of said wheel.
 2. The towingapparatus according to claim 1 wherein said attaching means comprises afirst circular member attached to said first frame and a second circularmember attached to said second frame, said first circular member andsaid second circular member being in concentric alignment enabling therotational movement of said first frame relative to said second frameabout said vertical axis.
 3. The towing apparatus according to claim 1wherein said apparatus further comprises a transmission supported bysaid first frame enabling the transmission of power from said motor tosaid transmission and then to said wheel assembly permitting the forwardand rearward motion of said towing apparatus.
 4. The towing apparatusaccording to claim 1 wherein said gripper assembly comprises: a firstarm attached to said second frame to engage the workpiece; a second armpivotably connected to said second frame; and a linkage assemblysupported by said second frame enabling the pivotal movement of saidsecond arm relative to said second frame so as to engage the workpiece.5. The towing apparatus according to claim 4 wherein said gripperassembly further comprises a cylinder connected to said second arm tofurther secure said second arm to the workpiece.
 6. The towing apparatusaccording to claim 1 wherein said gripper assembly comprises: a towframe connected to said second frame; a cradle supported by said towframe and adapted to retain a workpiece; means for tilting at least aportion of said tow frame; and means for activating said tilting means.7. The gripper assembly according to claim 6 wherein said tilting meanscomprises (i) a linkage assembly supported by, and displaceable relativeto, said tow frame, and (ii) wheels supported by said linkage assembly.8. The gripper assembly according to claim 6 wherein said activatingmeans comprises a hydraulic Jack supported by said linkage assembly. 9.The towing apparatus according to claim 1 wherein said apparatus furthercomprises a lock for restraining the rotational movement of said firstframe relative to said second frame.
 10. The towing apparatus accordingto claim 1 wherein said gripper assembly being adapted to engage thenosewheel of an aircraft.
 11. The towing apparatus according to claim 1, said gripper assembly being adapted to engage the tailwheel of anaircraft.
 12. The towing apparatus according to claim 1 wherein saidsecond axis being positioned above or below the first axis by no morethan about 40% of the radius of said wheel.
 13. The towing apparatusaccording to claim 12 wherein said second axis being positioned above orbelow the first axis by no more than about 20% of the radius of saidwheel.
 14. The towing apparatus according to claim 1 wherein said motorcomprises an internal combustion engine.
 15. The towing apparatusaccording to claim 1 wherein said motor comprises an electric motor. 16.The towing apparatus according to claim 1 wherein said motor comprisesan air motor.
 17. An apparatus for towing a workpiece comprising: afirst frame having a circular member; a second frame in spaced verticalrelationship to said first frame, and having a circular member so thatsaid circular member of said first frame rotatably engages said circularmember of said second frame enabling said first frame to rotate relativeto said second frame about a common substantially vertical axis; a wheelassembly supported by said first frame within said circular member ofsaid first frame and having a wheel for rotational movement about afirst axis; a motor supported by said first frame to power said wheelassembly; a handle assembly attached to said first frame to rotate saidfirst frame relative to said second frame; and a gripper assemblysupported by said second frame and offset from said vertical axis,wherein said gripper assembly attaches to a workpiece for towing along asecond axis positioned between about 30% of the radius of said wheelabove to about 60% of the radius of said wheel below said first axis.18. The towing apparatus according to claim 17 wherein said apparatusfurther comprises a transmission supported by said first frame enablingthe transmission of power from said motor to said transmission and thento said wheel assembly permitting forward and rearward motion of saidtowing apparatus.
 19. The towing apparatus according to claim 17 whereinsaid gripper assembly comprises: a first arm attached to said secondframe to engage the workpiece; a second arm pivotably connected to saidsecond frame; and a linkage assembly supported by said second frameenabling the pivotal movement of said second arm relative to said secondframe so as to engage the workpiece.
 20. The towing apparatus accordingto claim 19 wherein said gripper assembly further comprises a cylinderconnected to said second arm to further secure the second arm to theworkpiece.
 21. The towing apparatus according to claim 17 wherein saidgripper assembly comprises: a tow frame connected to said second frame;a cradle supported by said tow frame and adapted to retain a workpiece;means for tilting at least a portion of said tow frame; and means foractivating said tilting means.
 22. The gripper assembly according toclaim 21 wherein said tilting means comprises (i) a linkage assemblysupported by, and displaceable relative to, said tow frame, and (ii)wheels supported by said linkage assembly.
 23. The gripper assemblyaccording to claim 22 wherein said activating means comprises ahydraulic jack supported by said linkage assembly.
 24. The gripperassembly according to claim 22 wherein said activating means comprises apivotable lever assembly.
 25. The towing apparatus according to claim 17wherein said apparatus further comprises a lock for restraining therotational movement of said first frame relative to said second frame.26. The towing apparatus according to claim 17 wherein said gripperassembly being adapted to engage the nosewheel of an aircraft.
 27. Thetowing apparatus according to claim 17 , said gripper assembly beingadapted to engage the tailwheel of an aircraft.
 28. The towing apparatusaccording to claim 17 wherein said second axis being positioned betweenabout 40% of the radius of said wheel above to about 40% of the radiusof said wheel below said first axis.
 29. The towing apparatus accordingto claim 28 wherein said second axis being positioned between about 20%of the radius of said wheel above to about 20% of the radius of saidwheel below said first axis.
 30. An apparatus for towing a workpiececomprising: a first frame; a second frame in spaced verticalrelationship to the first frame; means for attaching said first frame tosaid second frame enabling rotational movement of said first framerelative to said second frame about a common vertical axis; a wheelassembly supported by said first frame and having a wheel for rotationalmovement about a first axis; a transmission supported by said firstframe; a motor supported by said first frame wherein said motortransmits power to said transmission and said transmission thentransmits said power to said wheel assembly permitting the forward andrearward motion of said towing apparatus; a handle assembly attached tosaid first frame to rotate said first frame relative to said secondframe; and a gripper assembly supported by said second frame and offsetfrom said vertical axis, said gripper assembly being positioned on saidsecond frame so as to engage a workpiece for towing along a second axispositioned above or below said first axis by no more than about 60% ofthe radius of said wheel.
 31. The towing apparatus according to claim 30wherein said attaching means comprises a first circular member attachedto said first frame and a second circular member attached to said secondframe, said first circular member and said second circular member beingin concentric alignment enabling the rotational movement of said firstframe relative to said second frame about said vertical axis.
 32. Thetowing apparatus according to claim 30 wherein said gripper assemblycomprises: a first arm attached to said second frame to engage theworkpiece; a second arm pivotably connected to said second frame; alinkage assembly supported by said second frame enabling the pivotalmovement of said second arm relative to said second frame so as toengage the workpiece; and a cylinder connected to said second arm tofurther secure the second arm to the workpiece.
 33. The towing apparatusaccording to claim 30 wherein said gripper assembly comprises: a towframe connected to said second frame; a cradle supported by said towframe and adapted to retain a workpiece; means for tilting at least aportion of said tow frame; and means for activating said tilting means.34. The towing apparatus according to claim 30 wherein said apparatusfurther comprises a lock for restraining the rotational movement of saidfirst frame relative to said second frame.
 35. The towing apparatusaccording to claim 30 wherein said gripper assembly being adapted toengage the nosewheel of an aircraft.
 36. The towing apparatus accordingto claim 30 , said gripper assembly being adapted to engage thetailwheel of an aircraft.
 37. The towing apparatus according to claim 30wherein said second axis being positioned above or below said first axisby no more than about 40% of the radius of said wheel.
 38. The towingapparatus according to claim 37 wherein said second axis beingpositioned above or below said first axis by no more than about 20% ofthe radius of said wheel.
 39. The towing apparatus according to claim 30wherein said motor comprises an internal combustion engine.
 40. Thetowing apparatus according to claim 30 wherein said motor comprises anelectric motor.
 41. The towing apparatus according to claim 30 whereinsaid motor comprises an air motor.
 42. An apparatus for towing aworkpiece comprising: a first frame having a circular member; a secondframe in spaced vertical relationship to said first frame, and having acircular member so that said circular member of said first framerotatably engages said circular member of said second frame enablingsaid first frame to rotate relative to said second frame about a commonsubstantially vertical axis; a wheel assembly supported by said firstframe within said circular member of said first frame and having a wheelfor rotational movement about a first axis; a transmission supported bysaid first frame; a motor supported by said first frame wherein saidmotor transmits power to said transmission which then transmits power tosaid wheel assembly permitting the forward and rearward motion of saidtowing apparatus; a handle assembly attached to said first frame torotate said first frame relative to said second frame; and a gripperassembly supported by said second frame and offset from said verticalaxis for attaching to a workpiece, wherein said gripper assemblyattaches to the workpiece for towing along a second axis positionedbetween about 60% of the radius of said wheel above to about 60% of theradius of said wheel below said first axis.
 43. The towing apparatusaccording to claim 42 wherein said gripper assembly comprises: a firstarm attached to said second frame to engage the workpiece; a second armpivotably connected to said second frame; a linkage assembly supportedby said second frame enabling the pivotal movement of said second armrelative to said second frame so as to engage the workpiece; and acylinder connected to said second arm to further secure the second armto the workpiece.
 44. The towing apparatus according to claim 42 whereinsaid gripper assembly comprises: a tow frame connected to said secondframe; a cradle supported by said tow frame and adapted to contact andretain a workpiece; means for tilting at least a portion of said towframe to the ground; and means for activating said tilting means. 45.The towing apparatus according to claim 42 wherein said gripper assemblybeing adapted to engage the nosewheel of an aircraft.
 46. The towingapparatus according to claim 42 , said gripper assembly being adapted toengage the tailwheel of an aircraft.
 47. The towing apparatus accordingto claim 42 wherein said second axis being positioned above or belowsaid first axis by no more than about 40% of the radius of said wheel.48. The towing apparatus according to claim 47 wherein said second axisbeing positioned above or below said first axis by no more than about20% of the radius of said wheel.
 49. In an apparatus for towing aworkpiece having a first frame, a second frame in spaced relationship tothe first frame, means for attaching the first frame to the second frameenabling rotational movement of the first frame relative to the secondframe, a wheel assembly, a motor to power the wheel assembly, and ahandle assembly attached to the first frame to rotate the first framerelative to the second frame, a gripper assembly comprising: a first armattached to said second frame to engage a workpiece; a second armpivotably connected to said second frame; a linkage assembly supportedby said second frame enabling the pivotal movement of said second armrelative to said second frame so as to engage the workpiece; and acylinder connected to said second arm to further secure the second armto the workpiece.
 50. In an apparatus for towing a workpiece having afirst frame, a second frame in spaced relationship to the first frame,means for attaching the first frame to the second frame enablingrotational movement of the first frame relative to the second frame, awheel assembly, a motor to power the wheel assembly, and a handleassembly attached to the first frame to rotate the first frame relativeto the second frame, a gripper assembly comprising: a tow frameconnected to said second frame; a cradle supported by said tow frame andadapted to retain a workpiece; means for tilting at least a portion ofsaid tow frame; and means for activating said tilting means.